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Discussion Starter · #1 ·
My boat has two fuel tanks. The one I've been using is a 40 gallon aluminum tank. I just replaced a 25 gallon rusty steel tank with an aluminium version I had built. I have a main engine and a generator. I can connect the main to the 40 gallon tank and then generator to the 25 gallon tank, but if I had my choice I'd be able to run either motor from either tank. If that's too complex, how should I set it up so I can transfer fuel either direction if needed?
 

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The thing to watch is the return (assume you have diesels). If you put valves in the lines and switch over the supply but not the return, the tank you are drawing from will be emptied and the other will be filling and may overflow. Best would be a pair of valves that work together and switch both supply and return at the same time.
 

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I have two tanks and solved the problem by plumbing the extra tank to go to the main tank. I always fill the main tank from the extra (unless both are empty) and fill the extra from the deck fill. That way neither tank has fuel sitting in it for long periods of time
 

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Discussion Starter · #5 ·
I have two tanks and solved the problem by plumbing the extra tank to go to the main tank. I always fill the main tank from the extra (unless both are empty) and fill the extra from the deck fill. That way neither tank has fuel sitting in it for long periods of time
How are they connected? Just a gravity feed? Transfer pump?
 

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I like having multiple tanks for both fuel and water. Redundancy in the event of a leak or clog or contamination. They should be fully independent and, as mentioned, use a manifold to isolate both the feed and return simultaneously.

You could send them both through the same pre-filter (ie RACOR), if you like, but making that redundant would be nice too.

I also like drawing one tank down to half, switching to the other and drawing it down to near empty, then switching back to the first. This way, I have a reserve until I get back to the first tank, when its time to top off. Concept works for water and fuel.
 

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One boat back we had 2 fuel tanks. In our case, it was plumbed with 4 separate valves, 2 supplies, and 2 return valves. As mentioned, it is important with this setup that the operator sets the return and the supply valves to the same tank to avoid the possibility of overfilling a tank with return fuel.

I guess you could in theory set the supply different than the return to move fuel from one tank to the other if you kept careful track of things.

The Groco valve mentioned solves the operator error problem.
 
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